This invention relates to thermosetting coating compositions containing at least one thermosettable polyester and an aminoplast resin together with a catalyst therefor comprising an alkali metal organosulfonate. This invention also relates to coatings and inks prepared from such compositions. Such inks are especially useful for imprinting metal containers e.g. beer cans, soda cans, etc.
Thermosetting coating compositions containing one or more thermosettable polyesters and an aminoplast resin are well known in the prior art. Typically, such prior art compositions are cured by means of acid catalysts. When such compositions are intended for use as coatings or inks, one or more pigments are added and the catalyst of universal choice is para toluene sulfonic acid ("PTSA"). However, coatings and inks prepared from such compositions have several disadvantages: (a) they require relatively high activation temperatures, e.g. 170.degree.-200.degree. C., thereby necessitating high energy costs and relatively low printing speeds; and (b) the compositions are not thoroughly cross-linked, and exhibit relatively poor resistance to abrasion and pasteurization (typically required for beer containers).
The disadvantages of the prior art compositions are overcome by use of an alkali metal sulfonate as the activation catalyst. Not only does the alkali metal sulfonate permit the use of lower activation temperatures, but many of the alkali metal sulfonates also possess excellent dispersing properties, thus resulting in better wetting of the pigment in the composition and thereby resulting in improved transferability of the coating or ink to the substrate, as well as improved flow properties.